Compared with a conventional macro base station, a whole system of a remote-radio distributed base station is divided into two parts, namely, a baseband processing unit BBU (Baseband Unit) and a remote radio frequency unit RRU (Remote RF Unit). The RRU is placed at an access point far away from the BBU, the RRU and the BBU are connected through an optical fiber and transmit a wireless baseband signal in an analog or digital manner, and a distance between the BBU and the RRU is generally tens of meters to one or two hundred meters. In this way, network construction of a system becomes more flexible and convenient, antenna installation is not influenced by an equipment room location, and it is also convenient to design large capacity for a base station system, which facilitates reduction of system cost. A distributed antenna system DAS (Distributed Antenna System) is similar to a remote-radio distributed base station, but a distance between a BBU and an RRU may be extended to several kilometers or even tens of kilometers, and in addition to a direct connection through an optical fiber, a connection through an optical transport network such as a PON (Passive Optical Network, passive optical network) or a WDM (Wave Division Multiplexing, wave division multiplexing) is also adopted. Furthermore, a multi-cell joint processing manner, such as network MIMO (multiple-input multiple-output system) or multi-cell joint scheduling, is preferably adopted to reduce inter-cell interference, thereby further increasing system capacity.
With the emergence of 3G/4G technologies such as LTE, wireless spectra become increasingly wider (20 MHz-100 MHz), and meanwhile, with wide application of multi-antenna technologies such as MIMO, an increasingly greater bandwidth is required for transmitting a wireless baseband signal between the BBU and the RRU. Taking the LTE as an example, for a bandwidth of 20 MHz, 2048-point FFT is adopted, a sub-carrier interval is 15 KHz, and a sampling rate of baseband signals is 2048×15 KHz=30.72 Msps, and for an RRU with 4×4 MIMO configuration, 16-bit ADC/DAC (analog to digital conversion/digital to analog conversion) is adopted, and a transmission line between the BBU and the RRU adopts 8B/10B coding, and therefore, a bit rate of an uplink/downlink baseband signal is up to: 30.72 (Msps)×4 (antenna)×16 (bit)×2 (I/Q component)/(8/10)≈5 Gbps.
Therefore, effectively compressing a wireless baseband signal to reduce a baseband signal transmission bandwidth between a BBU and an RRU is an important requirement.